Thermionically-active substance



W. WILSON.

THERMIONICALLY ACTIVE SUBSTANCE.

APPLICATION FILED AUG- 12. 1918.

1A1 9,5300 Patented June 13, R922.

6' m F j 2 mwfii'om- M/xY/fmv M07501? UNHTED STATES PATENT @FFHQE.

WILLIAM WILSON, OF EAST ORANGE, NEW JERSEY, ASSIGNOR 'ro WESTERN ELEQTRIU COMPANY, INCORPORATED, on NEW YORK, N. Y., A CORPORATION on NEW YOR,K

THEBMIONICALLY-ACTIVE SUBSTANCE.

Specification of Letters Patent.

Patented June 13, 1922.

Application filed August 12, 1918. Serial No. 249,523.

To all whom it may concern:

Be it known that I, IVILLIAM VVILSON, a subject of the King of Great Britain, residing at East Orange, in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in T hermionically-Active Substances, of which the following is a full, clear, concise, and exact description.

This invention relates to thermionically active substances which may serve as a source of electrons in a thermionic device, such as an audion. It has been known for some time that platinum filaments coated with alkaline earth oxide have a high order of thermionic activity. An object of the present invention is to subject ductile metals.

of the iron group such as iron, nickel or cobalt to a special treatment whereby their thermionic activity is increased and made comparable to that of oxide-coated platinum filaments.

As disclosed in the patent to Nicolson & Hull,No. 1,209,324, December 19, 1916- electron emitting cathodes and the process of manufacturing the same, a platinumcoated filament having a high order of activity may be made by applying alternate coatings of carbonate or oxide of barium or strontium, the coated filament being finally baked in the. open air for about two hours. It has been discovered that ifthis process is applied to a metal of. theiron group, while its activity may be increased, it is not increased nearly as much as in the case where the coating is finally baked either (a) in absence of oxygen or (b) baked in air on the filament for a comparatively short period, for instance, from one to five minutes.

It is desirable that clean or pure metal should be employed as the core or body of the filament and accordingly the metal of the iron group which is chosen, if not already clean, may be cleaned by pre-glowing in vacuo, or in the absence of oxygen at a high temperature, and then coated. In the pre-glowing, a pressure which varies from .1 to .0001 mm. has been used. It is only necessary to maintain the filament at a high or flashing temperature for a short time, viz, about five seconds.

After the filament has been pre-glowed,

it is not essential that it be coated in the particular way outlined' above. For instance, the filament may be coated by sputter ng the coating material on the filament. This is done by placing the filament near the coat ng'material, both being in vacuo. The coating material is heated and it sputters and deposits on the hot filament.

\Vhen the filament is cleansed as indicated above by flashing in vacuo or in the absence of oxygen, occluded gases are driven out of the filament and any oxides that are on the filament are reduced. Best results are obtained if the filament is kept in this condition, and to this end, after the filament has been cleansed in this manner, all subsequent heating of the filament should be in vacuo or 1n the absence of oxygen, to prevent reoxldation and re-absorption of gasses. In certain cases it may be sufiicient to perform the above process of flashin and baking in the absence of oxygen. It 1s not necessary that the filament be cleaned as indicated above, and metal which has been rendered chemically pure byany other process may be used instead.

Apparatus that may be used in carrying out both the pre-glowing and the sputtering processes. is shown in the figure of the drawing in which a boat 1 of molybdenum, for instance, contains the coating oxide or material 2 with which it is desired to coat the filament 3. This coating material may be a mixture of strontium and barium oxides for instance. The boat 1 and the filament 3 are sealed into a glass tube 4-, and may be heated electrically by current from the sources of current 5- and 6, respectively. The glass tube 4 is provided with an outlet 7 through which it may be evacuated.

During evacuation of the glass tube, the filament and the boat are heated to a high temperature, this pre-glowing serving to clean its surface thoroughly. The fiament is then allowed to cool and the molybdenum boat heated to a high temperature (more than two thousand degrees C.). Some of the coating material 2 sputters or evaporates and is condensed on the filament.

Another method which may be employed for coating the filament is as follows:

The metal which is to be employed as the core or body of the filament should be obtained as metallurgically pure as possible. This metal is reduced to the form of a twisted filament as shown in the Nicolson- Hull Patent No. 1,2093%, supra, and as disclosed therein, this filament may be suspended between two electrodes, for supplying current which passes through the filament to heat it. The filament is given a total of sixteen coats of carbonates of barium and strontium, applied in the following order:

4 coats of SrcO 4 coats of BaCO 4: coats of SrOO l coats of BaCO Between the application of each coating, the wire should be flashed at a red heat and after the final coating has been applied the filament is baked in the open air for a short time, for instance, about three minutes, the temperature of the filament being low enough that only a relatively small amount of oxidation of the body or core of the filament takes place.

The coating material may be applied in an aqueous solution as disclosed 1n Nicolson-Hull Patent No. 1,209,32 l, or parafiine may be used as a carrier for the coating material as described and claimed in Hooker application Serial No. 252,689, filed September 5, 1918. In this case the strontium carbonate and barium carbonate are thoroughly mixed and stirred into separate batches of paratfine. The stirring may be continued until the paratfine is sufiiciently cool to congeal, after which it may be worked into small rods which can be placed upon suitable holders for application to the heated filament. The paraffine melts on coming in contact with the hot filament and a portion of the alkaline earth compound is deposited on the filament. Flashing the filament as indicated above, during the coating process serves to burn ofi' the parafline and to reduce to the filament.

the carbonate to the oxide which adheres First a parafiine rod containing strontium carbonate is employed to apply four coats to the filament, then a parafiine rod containingbarium carbonate to give four coats more, etc., until a suitable coating of the desired thickness has been provided.

A filament made as indicated above may be employed as the cathode of a thermionic amplifier connected as shown in the patent to Arnold, No. 1,129,942, March 2, 1915.

This application is a continuation in part of my copending application No. 182,965, filed July 26, 1917, for method of making thermionically active substances.

The apparatus described but not claimed in this application for coating a filament is claimed in the copending application of E. R. Stoekle, Serial No. 527,178, filed January 5, 1922.

lVhat is claimed is:

1. A filament comprising a core of a duotile metal of the iron group and a coating of strontium and barium oxides, said filament having a degree of thermionic activity comparable to that of a platinum filament similarly coated and operated under similar conditions.

2. A filament comprising a core of nickel and a coating of strontium and barium oxides, said filament having a degree of thermionic activity comparable to that of a platinum filament similarly coated and operated under similar conditions.

In witness whereof, I hereunto subscribe lrgyl sname this 6th day of August A. D.,

WILLIAM WILSON.

DIISGLAHMER 1,419,530.William Wilson, East Orange, N. J.

June 13, 1922. Telephone and Telegraph Company.

to claim 2 of said Letters Patent, to wit:

STANCE. Patent dated the assignee, Amemcan Hereby enters this disclaimer THERMIONICALLY ACTIVE SUB- Disclaimer filed May 16, 193 1, by

2. A filament comprising a core of nickel and a coating of strontium and barium oxides, said filament having a degree of thermionic activity comparable to that of a platinum filament similarly coated and operated under similar conditions.

[Ofiicial Gazette Jane 5, 1.984.] 

